1. Field of the Invention
The present invention relates to an electrically conductive material for connecting parts, such as a terminal for connectors or a bus bar used mainly for electrical wiring in automobiles, household equipment, and the like, and also to a mating-type connecting part and a method for producing the same. The present invention particularly relates to an electrically conductive material for connecting parts and a mating-type connecting part, which are expected to have both reduced friction or abrasion upon the insertion and extraction of male and female terminals and electrical connection reliability in use, and a method for producing the same.
2. Description of the Related Art
JP-B-3926355 describes an electrically conductive material for connecting parts, which has high electrical reliability (low contact resistance) and a low friction coefficient and is suitable as a terminal for a mating-type connector. According to the invention of JP-B-3926355, a copper-alloy plate strip having higher surface roughness than ordinary copper-alloy plate strips is used as a base material, and, on the surface of the base material, a Ni plating layer, a Cu plating layer, and a Sn plating layer are formed in this order, a Cu plating layer and a Sn plating layer are formed in this order, or only a Sn plating layer is formed. The Sn plating layer is reflowed so that a Cu—Sn alloy layer is formed from the Cu plating layer and the Sn plating layer or from the copper alloy base material and the Sn plating layer. At the same time, a portion of the Cu—Sn alloy layer is allowed to expose on the surface through the Sn plating layer smoothed by reflowing (a portion of the Cu—Sn alloy layer is exposed in the area of projections of the depressions and projections formed on the base material surface).
In JP-B-3926355, the electrically conductive material for connect parts formed after reflowing has, as a surface coating layer, a Cu—Sn alloy layer and a Sn layer, or alternatively a Ni layer, a Cu—Sn alloy layer, and a Sn layer, in this order. In some cases, a Cu layer remains between the base material surface and the Cu—Sn alloy layer or between the Ni layer and the Cu—Sn alloy layer. According to JP-B-3926355, the Cu—Sn alloy layer and the Sn layer are formed on the outermost surface (the Cu—Sn alloy layer exposure area ratio on the surface is 3 to 75%), the average thickness of the Cu—Sn alloy layer is 0.1 to 3.0 μm, the Cu content is 20 to 70 at %, and the Sn layer has an average thickness of 0.2 to 5.0 μm. It is also mentioned that the arithmetic mean roughness Ra of the base material surface is 0.15 μm or more at least in one direction, and is preferably 4.0 μm or less in every direction, and that the Cu—Sn alloy layer exposure interval on the surface is preferably 0.01 to 0.5 mm at lease in one direction.
JP-B-4024244 describes an electrically conductive material for connecting parts, which is the subordinate concept of JP-B-3926355, and a method for producing the same. The plating layer configuration and the coating layer configuration after reflowing themselves are the same as in JP-B-3926355. According to JP-B-4024244, in the electrically conductive material for connecting parts formed after reflowing, a Cu—Sn alloy layer and a Sn layer are formed on the outermost surface (of the surface coating layer, the Cu—Sn alloy layer exposure area ratio on the surface is 3 to 75%), the Cu—Sn alloy layer has an average thickness of 0.2 to 3.0 μm and a Cu content of 20 to 70 at %, the Sn layer has an average thickness of 0.2 to 5.0 μm, and the arithmetic mean roughness Ra of the base material surface is 0.15 μm or more at least in one direction and is 3.0 μm or less in every direction. It is also mentioned that the arithmetic mean roughness Ra of the base material surface is 0.3 μm or more at least in one direction, and is preferably 4.0 μm or less in every direction, and that the Cu—Sn alloy layer exposure interval on the surface is preferably 0.01 to 0.5 mm at lease in one direction.
JP-A-2007-258156 describes an electrically conductive material for connecting parts, which basically inherits the technical concepts of JP-B-3926355 and JP-B-4024244 and has improved solderability, and a method for producing the same. In the invention, the plating layer configuration and the coating layer configuration after reflowing themselves are basically the same as in JP-B-3926355 and JP-B-4024244. However, unlike JP-B-3926355 and JP-B-4024244, the invention may encompass the case where the Cu—Sn alloy layer is not exposed (only a Sn layer is present on the outermost surface). In this application, an electrically conductive material for connecting parts formed after reflowing is specified as follows. Of the surface coating layer, the Ni layer has an average thickness of 3.0 μm or less, the Cu—Sn alloy layer has an average thickness of 0.2 to 3.0 μm, the Sn layer has, in a vertical cross-section of the material, a minimum inscribed circle diameter (D1) of 0.2 μm or less and a maximum inscribed circle diameter (D2) of 1.2 to 20 μm, and the altitude difference (Y) between the outermost point of the material and the outermost point of the Cu—Sn alloy layer is 0.2 μm or less. JP-A-2007-258156 further mentions that it is preferable that when (D1) is 0 μm (when a portion of the Cu—Sn alloy layer is exposed, and the outermost surface is formed of the Cu—Sn alloy layer and the Sn layer), the Cu—Sn alloy layer has a maximum inscribed circle diameter (D3) of 150 μm or less on the material surface and/or the Sn layer has a maximum inscribed circle diameter (D4) of 300 μm or less on the material surface.
Meanwhile, JP-A-2004-300524, JP-A-2005-105307 and JP-A-2005-183298 state that a copper-alloy plate strip is stamped and then entirely plated with Sn, i.e., post-plated, so that a Sn plating layer is formed also on the stamped end face, thereby improving the solderability of a terminal or the like as compared with the case where a copper-alloy plate strip is plated with Sn prior to stamping (pre-plated).
Further, JP-A-2008-269999 and JP-A-2008-274364 mention that a post-plated terminal has improved electrical reliability (low contact resistance), a reduced friction coefficient at a mating portion, and also improved solderability at a soldering portion.
According to the invention of JP-A-2008-269999, a terminal is formed in such a manner that only a mating portion has increased surface roughness, and then a Ni plating layer, a Cu plating layer, and a Sn plating layer are formed in this order, a Cu plating layer and a Sn plating layer are formed in this order, or only a Sn plating layer is formed. The Sn plating layer is reflowed so that a Cu—Sn alloy layer is formed from the Cu plating layer and the Sn plating layer or from the copper alloy base material and the Sn plating layer. At the same time, a portion of the Cu—Sn alloy layer is allowed to expose on the surface through the Sn plating layer smoothed by reflowing (a portion of the Cu—Sn alloy layer is exposed in the area of projections of the depressions and projections formed on the base material surface). At this time, the plating thickness is the same over the entire surface. At the mating portion, the Cu—Sn alloy layer and the Sn layer are formed on the outermost surface (the Cu—Sn alloy layer is exposed on the surface), and, therefore, there is a problem in terms of solder wettability. However, at other portions than the mating portion, there are no depressions or projections. Therefore, no Cu—Sn alloy layer is exposed (only a Sn layer is present on the outermost surface), and solder wettability is thus excellent.
According to the invention of JP-A-2008-274364, a copper alloy material with high surface roughness is stamped into a terminal piece, and then a Ni plating layer, a Cu plating layer, and a Sn plating layer are formed in this order, a Cu plating layer and a Sn plating layer are formed in this order, or only a Sn plating layer is formed. The Sn plating layer is reflowed so that a Cu—Sn alloy layer is formed from the Cu plating layer and the Sn plating layer or from the copper alloy base material and the Sn plating layer. At the same time, a portion of the Cu—Sn alloy layer is allowed to expose on the surface through the Sn plating layer smoothed by reflowing (a portion of the Cu—Sn alloy layer is exposed in the area of projections of the depressions and projections formed on the base material surface). In this case, the Sn plating layer at the soldering portion is formed thick. As a result, the Cu—Sn alloy layer is not exposed on the surface at the soldering portion, leading to excellent solder wettability.